The present invention relates generally to anode devices used to inhibit corrosion in metal water heater tanks and other metal liquid storage vessels and, in a preferred embodiment thereof, more particularly relates to a specially designed resistored anode assembly useful in this corrosion-inhibiting application.
Conventional metal water heater tanks, like other types of metal vessels used to store liquids, are subject to corrosion during use. To inhibit this corrosion, sacrificial anodes, normally constructed of magnesium, aluminum or zinc, are inserted into the tank. The sacrificial anode is slowly consumed during the corrosion protection process while generating an electrical current. As the anode is slowly depleted, its simultaneously generated electrical current cathodically protects the tank against corrosion.
The service life of the anode tends to be inversely dependent upon the amount of electrical current it generates in cathodically protecting the tank. In many fresh water supplies, particularly those having a high mineral content, the current flow generated by the anode is relatively high, resulting in a corresponding decrease in the useful life of the anode. In order to control the rate of consumption of a sacrificial anode, various anode constructions have been proposed in which a resistor is incorporated in the anode, and electrically connected between the anode and its protected tank, to automatically regulate the electrical current generated by the anode during its operation and thereby increase the service life of the anode.
While these resistored anode devices typically extended anode life, many of them also tended to be of a relatively complex construction, rather difficult to assemble, and relatively expensive to fabricate.
Many of these problems are essentially eliminated by a prior art sacrificial anode assembly that incorporates, in a simplified manner, an ordinary barrel-type carbon resistor into the interior of the assembly. This prior art anode assembly includes a cylindrical plastic insulating sleeve captively retained within the metal cap portion of the anode assembly and having a closed end with a central opening through which an end portion of the metal anode body core rod extends. A diametrically extending groove, which intersects the central sleeve opening, is formed in the closed sleeve end.
The cylindrical resistor body is disposed in a radial portion of the sleeve end groove, with one of the resistor end leads being radially extended over the anode rod end and soldered thereto. The other resistor end lead passes through an axially extending exterior side surface groove in the insulating sleeve and is soldered at its outer end to an external metal cap portion of the anode assembly.
Although this method of operatively positioning a resistor in a sacrificial anode assembly provides a worthwhile reduction in assembly time and cost, and provides the desired regulation of anode current generation, it has been found that it can create a problem relating to the structural integrity of the completed anode assembly. Specifically, it has been found that in certain shipping orientations of the tank in which the anode assembly is installed, harmonic vibrations may be created within the central anode core rod which are transmitted to the solder joint connecting a resistor end lead to the rod. These vibrations can fatigue and break the rod/lead solder joint, thereby rendering the anode assembly inoperative.
From the foregoing, it can be seen that it would be desirable to provide a sacrificial anode assembly, of the type having an insulating sleeve-installed resistor as generally described above, which substantially eliminates this vibration-caused solder joint breakage problem. It is accordingly an object of the present invention to provide such a sacrificial anode assembly.